/in/foo.cc:10:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main(){
      ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:14:22: error: 'abs' was not declared in this scope
   if(++a>=11&&abs(d-f)>1)h[++j]=d,h[++j]=f,a=d=f=0;
                      ^
/in/foo.cc:14:22: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/cmath:103:5: note:   'std::abs'
     abs(_Tp __x)
     ^~~
/in/foo.cc:15:22: error: 'abs' was not declared in this scope
   if(++b>=21&&abs(e-g)>1)i[++k]=e,i[++k]=g,b=e=g=0;
                      ^
/in/foo.cc:15:22: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/cmath:103:5: note:   'std::abs'
     abs(_Tp __x)
     ^~~